(x方y方+1)的平方-4x方y方
问题描述：
(x方y方+1)的平方-4x方y方
答
（x²y²+1）²-4x²y²
=（x²y²）²+1+2x²y²-4x²y²
=（x²y²）²+1-2x²y²
=（x²y²-1）²
=[(xy-1)(xy+1)]²
=(xy-1)²(xy+1)²